Fracture and failure prediction of textile composites using mechanism-based models

Qingda Yang, Brian N. Cox

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Predicting the mechanical responses of a composite beyond its linear elastic regime and up to the ultimate failure point remains a challenging issue in laminar composite engineering and design. Multiple failure events happen during the post elastic deformation regime. These include matrix failure in resin-rich pockets, intra-tow tunnelling crack, inter-tow delamination crack, fiber rupture (in tension)/buckling (in compression) and, for laminar composites, interlaminar debonding. The first four modes are considered as in-plane modes that typically occur within an individual ply; while the last one is labelled as an out-of-plane mode that involves interplay between plies. The complex interaction of these damage modes, which depends on the constituent materials, stacking sequence, geometry and loading configuration, governs the macroscopic mechanical response of a composite component. It can be shown that each of these failure modes has a certain length scale associated with it and the failure is related to the local stress states that are greatly influenced by local fiber arrangement. It would be a formidable task if all these textile details have to be resolved fully before one can predict the failure. Fortunately, recent development on the so-called Binary Model has led to the conclusion that such details need not be fully accounted in composite failure analysis. Rather, macroscopic mechanical properties and failure strengths can be assessed using lowest order representation of fiber tows that are embedded in an effective medium describing the spatial dimension of a textile composite. By introducing a proper gage length for local stress/strain averaging, the spatially averaged stresses/strains can be correlated to many of the failure events, allowing for failure prediction. In this paper, the rationale that leads to the use of spatial averaging will be discussed and some validations of the method will be presented. The out-of-plane mode, interlaminar debonding, is also of extreme importance for composite design and it has been extensively studied in the past using classic linear elastic fracture mechanics (LEFM). Most of such studies treated it as an isolated failure event that is NOT coupled to other in-plane failure modes, which is often not the case in reality. Furthermore, the LEFM view of fracture process as a point-process has been proved over-simplistic. A trend in the last decade favours models in which nonlinear failure processes are represented explicitly, rather than being assigned to a point process. This is the so-called cohesive zone model formulation, which uses both material strength and an energy-based failure criterion (such as fracture toughness) to describe a failure event. This naturally includes a length scale in its formulation, which makes it an excellent alternative for delamination analyses of laminar composites. A 3D mode-dependent, irreversible cohesive zone model for interlaminar fracture will be formulated and its application to laminar composite will be discussed in this paper.

Original languageEnglish
Title of host publicationInternational SAMPE Technical Conference
Volume2005
StatePublished - Dec 1 2005
Externally publishedYes
EventSAMPE Fall Technical Conference - 37th ISTC - Seattle, WA, United States
Duration: Oct 31 2005Nov 3 2005

Other

OtherSAMPE Fall Technical Conference - 37th ISTC
CountryUnited States
CitySeattle, WA
Period10/31/0511/3/05

Keywords

  • Composites
  • Damage
  • Delamination
  • Failure mechanisms
  • Fracture

ASJC Scopus subject areas

  • Building and Construction
  • Chemical Engineering(all)
  • Polymers and Plastics
  • Chemical Engineering (miscellaneous)

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